1. Field of the Invention
The present invention relates generally to a wafer retrieval method in a multiple slicing wire saw, and more particularly to a wafer retrieval method in a multiple slicing wire saw which separates wafers, which were sliced simultaneously from different kinds of ingots by a wire saw, from slice base mounting beams to which the wafers are adhered, and retrieves the individual wafers.
2. Description of Related Art
An example of an ingot slicing apparatus is a wire saw. The wire saw presses an ingot against wire rows, which are running at a high speed, and supplies slurry to a contact area where the ingot is in contact with the wire rows to thereby slice the ingot into a number of wafers.
The wire saw normally slices one ingot in one slicing operation, but recently, a multiple cutting method has been adopted to slice a number of ingots at the same time in order to improve the slicing efficiency.
As shown in FIG. 10, a plurality of ingots Ia, Ib, Ic (three ingots are illustrated in FIG. 10) are adhered in series to the mounting plate M through slice base mounting beams Sa, Sb, Sc. In this method, a plurality of ingots can be sliced efficiently at the same time.
Incidentally, all the wafers, which have been sliced from the ingot by the wire saw, are adhered to the slice base mounting beams. Thus, it is necessary to separate the wafers from the slice base mounting beams after the slicing so that they can be individual wafers.
In a conventional separating method, the wafers are soaked in hot water so that they can be separated from the slice base mounting beams (a natural separating method). In this method, all the wafers are separated from the slice base mounting beams at the same time, and they are stored in a cassette, which is placed in a hot water tank.
In the conventional separating method, all the wafers are separated at the same time. For this reason, the separated wafers are mixed within the cassette, and different kinds of wafers are undistinguishable from one another.